Means for preventing retrcactive effects in audion amplifier circuits



G. A. SOMERSALO MEANS FOR PREVENTING RETROACTIVE EFFECTS IN AUDIONAMPLIFIER CIRCUITS Filed Feb. 11. 1926 INVENTOR C-f-eowcrz /-7.SOMERSHLO ATTORNEYS June 211, Eg

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GEQEGE A. SQ'MERSALO, F NEW YORK, N. Y.

Application filed February 11, 1926. Serial No. 87,608.

This invention relates to the amplification of electric currents ofminute intensities such as experienced in the reception of radiotelephonic and telegraphic signals by means a of audion tubes of thethree-electrode type, and more particularly to the provision of meansfor neutralizing, balancing, or otherwise compensating for the inherentcapacity coupling between the input and output elecm trodes of theaudion tubes of the amplifier.

It has long been known that when audion tubes are energized and thefilament and grid electrodes connected to a source of alternatingsignalenergy, and the filament and plate electrodes connected to asuitable output circuit, that the variations in the output circuit arefed back into the input circuit, due to the inherent capacity couplingexisting between the electrodes contained in the input and outputcircuits. These current variations fed back into the input circuit may,and frequently do, cause oscillations which, in amplifiers, areparticularly objectionable since they interfere considerably with thereception of the incoming signals and frequently rise to such magnitudesas to completely incapacitate the amplifier.

In my co ending applications Ser. No. 18,019, filed arch 24, 1925, andSer. No.

89 87,607, filed February 11,1926, I have secured'the desired balancebetween the input and output circuits by means of a network whichincludes a con ling between one end of the input coil an a ointintermediate 85 the ends of the output in uctance, the point ofconnection to the output inductance being predetermined to establish aratio between the turns of the output inductance on opposite sides ofthe point of connection equal to 40 the inverse ratio between theinherent capacities of the audion tube. However, a balanced conditioncan also be obtained by a different network using a direct connectionfrom the low potential" end of the input in- 445 ductance to the platethrough a suitable condenser, and arranging in this connection aninductance which is inductively coupled to the output inductance betweenthe plate and the filament. This coupling is of such character that theratio of inherent capacitiei between the electrodes of the audion bearsa(361428.111 definite relation to the mutualinductance of this coupling.The network may thus be balanced either by means of a variable condenserwhich changes the ratio of the inherent capacities of the audion, or byvarying the mutual inductance of the coupling.

In the accompanying drawings- Fig. 1 is a diagram of a network for asingle amplifier unit in which my invention is embodied in one form;

Fig. 2 is a similar view in which my invention is embodied in anotherform;

Figs. 3 and 4 are diagrams of further 55 modified forms.

Referring to the drawings, particularl to Fig. 1, I have illustrated theusual au ion electrodes, viz, plate 1, grid 2 and filament 3, inputinductance 4 and output inductance 5. The input coil 4 is connected atitshi'gh potential end directly with the grid electrode 2. At its lowpotential end it is connected by line 6 with the plate electrode 1through an inductance 7 and condenser 8. The output inductance 5 isarranged in the connection 9 from the battery B to the plate 1, thenegative side of the battery being connected to the filament 3. Thelatter is, as usual, energized by its battery A. A tuning condenser T isbridged across the input inductance 4. 1

The coils 5 and 7 in the output circuit have a mutual inductance. Whenthe ratio of this mutual inductance to the self-inductance of the coil 5is equal to the ratio of the inherent capacity between the grid andfilament electrode to the sum of this capacity plus the capacity betweenthe grid and plate electrodes, the network is balanced. In order 9 toestablish this equality of ratios, I v rovide in the layout shown in'Fig. 1 a b ancin condenser 10. arran d between the plate an gridelectrodes, an by means of which the capacity between these electrodesmay be varied with respect to the capacity between the grid and thefilament electrode. The

ratio of capacities may thus be made to correspond to the ratio ofmutual inductance between the coils 7 and 5 to the self-inductance ofthe coil 5.

Graphically stated, if the grid filament capacity (0,) bears 'a certainratio to thesum of thegrid-filament capacity plus the gridplate capacity(c l-0,), that ratio should be e ual to the ratio of the mutualinductance When this balance of ratios is established there can be nofeed back of current from the output connections to the grid or inputcoil, and consequently there can be no oscillations set up which giverise to the ob'ectionable squealing which occurs in an un alancednetwork.

InFig. 2 the adjustment of ratios is accomplished by varying the mutualinductance of the coils 5 and 7 instead of by varying the capacitiesbetween the electrodes, as in Fig. 1, and I have indicated this variablecoupling at 11. l

In order to establish a direct current path between the grid andfilament electrodes of the audion, any appropriate connection may beutilized. I have illustrated in Figures 1 and 2 a connection 12 in whichis interposed an appropriate high impedance 13, i. e., either a highresistance or choke coil, which will pass direct current.

In Fig. 3 I have eliminated the direct connection between the filamentand grid through the high impedance 13, and have established a directcurrent, low voltage connection through the output coil 7 and asupplementary coil 14 which may be also inductively coupled to the coils5 and 7. This arrangement ma be somewhat more economical to construcsince the three coils 5, 7 and 14 may be wound on the same tube.

InFig. 4 the coil 5 is replaced by a choking coil 15, and thealternating current flows now through only coil 14 instead of throughboth 14 and 5, as in Fig. 3.

In all the layouts the coil 7 is the balancing coil and is inductivelycoupled to the coil or coils in the alternating current path between theplate and filament.

It is understood that other specific networks which accomplish the sameresult, will readily occur to those dealing with the problem", which donot depart from what I claim as my invention.

I claim I 1. An audion amplifier network comprising an alternatingcurrent plate filament circuit including an output inductance, an inputcircuit between grid and plate connected to the output circuit at apoint between the late and the output inductance and includ- 1n aninductance inductivel coupled to the in uctance in the plate filamentcircuit whereby to neutralize the inherent capacity of the audionelectrodes, and means for preventing high direct current voltage fromreaching the grid.

2. An audion amplifier net work comprising an alternating current platefilament circult including an output inductance, an input circuitbetween grid and plate connected to the output circuit at a pointbetween the plate and the output inductance and including an inductanceinductivel coupled to the in uctance in the plate lament circuit,whereby to neutralize the inherent capacity of the audion electrodes byrelatively balancing the said capacities against said inductances, meansfor preventing high direct current voltage from reaching the grid, andmeans for varying the values of balanced elements of the net work.

3. An audion amplifier network comprising an alternating current platefilament circult including an output inductance, an input circuitbetween grid and plate connected to the output circuit at a pointbetween the plate and the output inductance and includin an inductanceinductively coupled to the in uctance in the plate filament circuitwhereby to neutralize the inherent capacity of the audion electrodes,and means for preventing high direct current voltage from reaching thegrid, and an external adjustable condenser for varying the ratio betweenthe inherent capacities of the plate grid and filament electrodes.

4. An audion amplifier network comprising an alternating current platefilament circuit including an output inductance, an input circuitbetween grid and plate connected to the output circuit at apoint'between the plate and the output inductance and ineluding an inputcoil, one terminal of which is connected to the grid and a second coilinterposed between the other end of said input coil and the late andinductively coupled to the output inductance whereby to neutralize theinherent capacity of the audionelectrodes, and means for preventing highdirect current voltage from reaching the grid.

5. An audion amplifier circuit comprising plate, grid, and filamentelectrodes, an output coil interposed between-plate and filamentelectrodes, an input coil, one terminal of which is connected to thegrid and the other terminal of which has an alternating currentconnection to the plate electrode, said connection being established toa point in the output circuit between the plate and the output coil, anda balancing coil arranged in said connection between input coil andplate electrode and inductively coupled to the output coil in theplate-filament circuit whereby to neutralize the inherent capacity ofthe audion electrodes. 4

6. Anaudion amplifier circuit comprising plate, grid, and filamentelectrodes, an output coil interposed-between plate and filamentelectrodes, an input coil, one terminal of which is connected to thegrid and the other terminal of which has an alternating currentconnection to the plate electrode said connection being established to apoint in the output circuit between the plate and the output coil, and abalancing coil arran ed in said connection between input coil and plateelectrode and inductively coupled to the output coil in theplate-filament circuit, to ether with means for varying the ratio 0electrical values between related elements of the network to preventretroactive eflect of the output circuit upon the input coil.

7. An audion amplifier circuit comprising plate, grid, and filamentelectrodes, an output coll interposed between plate and filamentelectrodes, an input coil, one terminal of which is connected to thegrid and the other terminal of which has an alternating currentconnection to the plate electrode, said connection being established toa point in the output circuit between the plate and the output coil,means in the said connection to prevent high direct current voltage fromreaching the grid electrode, and a balancin coil arranged in saidconnection between input coil and plate electrode and inductivelycoupled to the output coil in the plate-filament circuit whereby toneutralize the inherent capacity of the audion electrodes.

8. An audion receiving system comprising an alternating currentplate-filament circuit including an output inductance, an input circuitbetween grid and plate connected to the output circuit at a pointbetween the plate and the output inductance, a direct current connectionbetween grid and filament, and means for preventing retroaction of theoutput voltage upon the input circuit including an inductanceinductively coupled to the output inductance, said inductance being apart of the input circuit.

9. An audion receiving system comprising an alternating currentplate-filament circuit including an output inductance, an input circuitbetween grid and plate connected to the output circuit at a pointbetween the plate and the output inductance, a direct current connectionbetween grid and filament, means for preventing retroaction of theoutput voltage upon the input circuit including an inductanceinductively coupled to the output inductance, said inductance being apart of the input circuit, and ex- I ternal means for varying the ratiobetween the inherent capacities of the plate, grid and filamentelectrodes.

10. An audion receiving system comprising an alternating currentplate-filament circuit including an output inductance, an input circuitbetween grid and plate connected to the output circuit at a pointbetween the plate and the output inductance, a direct current connectionbetween grid and filament, means for preventing retroaction of theoutput voltage upon the in ut circuit including an inductance inactively coupled to the output inductance, said inductance being a partof the input circuit, and an external condenser connected between thegrid and a point in the plate filament circuit.

11. An electric wave receiving and amplifying system employing vacuum.tubes with plate, grid, and filament electrodes, and comprising analternating current platefilament circuit including an outputinductance, a resonant input circuit between grid and plate andconnected to the output circuit between the plate and the outputinductance, a direct current connection between grid and filament, andmeans for preventing retroaction of the output voltage upon the resonantcircuit including an inductance connected in series with said resonantcircuit between grid and plate, and inductively coupled to the outputinductance.

12. An electric wave receiving and amplifying system employing vacuumtubes with plate, grid, and filament electrodes, and comprising analternating current platefilament circuit includin an output inductance,a resonant input circuit between grid and plate and connected to theoutput circuit between the plate and the. output inductance, a directcurrent connection between grid and filament, means for preventingretroaction of the output voltage upon the resonant circuit including aninductance connected in series with said resonant clrcuit between gridand plate and inductively coupled to the output inductance, and anexternal condenser connected between the grid and one of the otherelectrodes.

13. An electric wave receiving and amplifying system employing vacuumtubes with plates, grid, and filament electrodes, and comprising analternating current platefilament circuit including an outputinductance, a resonant input circuit between grid and plate andconnected to the output circuit between the plate and the outputinductance, a direct current connection etween grid and filament, meansfor preventing retroaction of the output Volta e upon the resonantcircuit including an in uctance connected in series with said resonantcircuit between grid and plate and inductively coupled to the outputinductance, and an external condenser connected between the grid and apoint of the plate-filament circuit.

between the plate and the output inductance,

a direct current connection between grid and filament, and means forneutralizing the eflect of the output voltage upon said resonant inputcircuit, said means including an inductance connected in series withsaid resonant circuit between grid and plate and conductively coupled tothe out ut inductance, and means for varying t e characteristics of theinter-electrode couplings whereby to obtain such neutralizationforsubstantially all frequencies of the receivm GEORGE A. SOMERSALO.

